This invention relates to improvements in or relating to port switches.
A port switch includes n bidirectional I/O communication ports, where n&gt;2, each port having at least a first state in which it propagates a signal in a first direction and a second state in which it propagates a signal in a second direction, an addressable latch means having n outputs connected to the ports respectively for establishing the state of each port, and a router having n inputs connected to the n ports respectively and n outputs connected to the n ports respectively and including an addressable register means which can be loaded with data defining at least a first connection through the router between the ith router input (1&lt;=i&lt;=n) and the jth router output (1&lt;=j&lt;=n) and a second connection through the router between the kth router input (1&lt;=k&lt;=n and k.notident.i) and the lth router output (1&lt;=l&lt;=n and l.notident.j), and a switch means responsive to the data in the addressable register means for connecting the ith router input to the jth router output and for connecting the kth router input to the lth router input.
A known port switch is described in U.S. Pat. No. 5,751,764, the disclosure of which is hereby incorporated by reference herein.
A television post production facility comprises an ensemble of machines of various types, such as editors, digital video effects devices and video tape recorders (VTRs). During an editing session, the producer employs an editor to control the operations (playback, record, etc.) performed by the other machines to produce a final master tape. A first video tape recorder may be controlled by the editor when recording source material, and when dubbing the recorded material to a second VTR, the first VTR may control operation of the second VTR.
Each machine may have an RS-422 communication port for transmitting and receiving messages relating to operation of the machine. RS-422 specifies a 9-pin connection and defines a port that is active as being either controlled or controlling. A controlling port receives on pins 2 and 7 and transmits on pins 3 and 8 whereas a controlled port receives on pins 3 and 8 and transmits on pins 2 and 7. When a controlling port is connected to a controlled port, forward messages are transmitted from the controlling port to the controlled port on pins 3 and 8 and reverse messages are transmitted from the controlled port to the controlling port on pins 2 and 7. Ports of the same type are not connected together.
In a given post production facility, several editing sessions, each requiring use of an editor and two or more other machines, may be conducted at any given time, and during a given editing session, the producer might wish to add machines to, and drop machines from, the suite of machines that are being used in the session. In order to allow an ensemble of machines to be interconnected in a flexible fashion in different suites, without needing to swap cables whenever a change is desired, the RS-422 ports of the machines may be connected to respective ports of a port switch.
The suite might be composed of only two machines, in which case one machine, designated a source machine, transmits command messages over a forward path and the other machine, designated a destination machine, transmits response messages over a reverse path. The connection between the source machine and the destination machine is referred to as a non-distributed connection. More generally, however, the suite contains at least three machines. One source machine transmits command messages to two or more destination machines, which generate response messages. In order to prevent a collision of response messages, a single destination machine is designated as the responding machine and the response messages of the other destination machines are blocked. Such a connection is referred to as a distributed connection.
When a machine in a distributed connection is assigned to a new connection, it is necessary to ensure that all destination machines in the current connection, and not just the responding destination machine, are disconnected in order to avoid undesired operation. It is not possible to poll the destination machines, because the response messages from the non-responding destination machines are blocked. Therefore it is normal practice to keep track of the current configuration of the suite.
U.S. Pat. No. 5,751,764 discloses a method for controlling the ports of a port switch using forward and reverse memories, each having one addressable location for each port of the port switch. The contents of the forward memory for a given port indicate whether the port is in use and, if so, whether it is a source or a destination, i.e. whether the port is connected to a source machine or a destination machine, and the contents of the reverse memory for a given port indicate whether the destination is a responding destination or a non-responding destination. In order to break down a distributed connection involving a given source machine, it is necessary to check the connection status of every port of the port switch in order to identify all the destination machines that are connected to the source machine. This is done by scanning the entire contents of the reverse memory. Then, each connection is broken. The operation of checking the status of each port is time consuming and imposes restrictions on the speed at which the port switch can be reconfigured. In some types of operation, it may be desirable to select a port for only a very short interval, for example a few frames of video material, and then release the port so that the associated machine will be available to other suites. This requires that it be possible to reconfigure the port switch at very rapidly, sometimes in as short a time as one vertical interval of a video signal (16.67 ms in the case of signals in the NTSC format).